Temperature and pressure dependence of the transverse-optic modes of ionic crystals and their associated anharmonic self-energies

Lowndes, R. P.; Rastogi, A. K.

doi:10.1103/physrevb.14.3598

Cited by 89 publications

(29 citation statements)

References 37 publications

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“…Accordingly we believe that oJ2 emission values (~2e) are more likely to be related to the crystal mode distribution, and actually we found [4] the following surprising occurrence: ~2e values are very close to the transverse optical frequencies ~T. We present in table I detailed data for ~2e and eOT [10] , for the emission band halfwidth H(0) at the lowest temperatures, and for the Huang-Rhys factor S (Se for the emission process) determined on the basis of the well-known relationship Please note that ~ values were obtained in ref. [2,11,12] by (2) and, more correctly, in [13], by using the shape function of the emission; finally, an accurate O)2e value in RbC1 was found by Brada [14], by also taking into account the relative changes between E(T) and H(T) as a function of T. We were [4] not able to give a conclusive explanation of the above occurrence.…”

Section: H~l) E(t) = E(o) -B Ctgh ~ (2) ( Ho~2 ) H 2 (T) = H 2 (0) mentioning

confidence: 76%

Speculations on the absorption and emission properties of the F-centre in alkali halides

Bosi

Nimis

1991

Il Nuovo Cimento D

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(ricevuto il 21 Febbraio 1991; revisionato il 18 Luglio 1991; approvato il 29 Luglio 1991) Summary. --A review of acquisitions and of unresolved problems concerning Fcentres in alkali halides is presented. The main conclusions are a) the temperature dependence of the bands is mainly due to the thermal expansion for the absorption process and to electron-phonon interaction for the emission process: for the latter half-width and Huang-Rhys factor values are related to the transverse optical frequency ones; b) the lifetime VR of the relaxed excited state is not intrinsic at low temperature because of the interaction between F-and a-centres always present in real samples; c) even though the absolute quantum yield decreases when F-centre concentration increases, the relative quantum yield vr is unaffected by change on F-centre concentration, strongly evidencing a nonhomogeneous distribution of F-centres in real samples; d) a temperature-dependent fine structure in zR (an Vr) values is observed but only when temperature control of the samples is better than a few hundredth of a degree: this effect has been interpreted in terms of interactions which involve F-, a-and F'-centres. PACS 61.70 -Defects in crystals. PACS 61.70.Dx -Colour centres.

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Section: H~l) E(t) = E(o) -B Ctgh ~ (2) ( Ho~2 ) H 2 (T) = H 2 (0) mentioning

confidence: 76%

Speculations on the absorption and emission properties of the F-centre in alkali halides

Bosi

Nimis

1991

Il Nuovo Cimento D

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“…32,39-44 n ϱ , E x0 , and 0 have been taken as adjustable parameters for these fits, while for the frequency of the optical phonon the values of Ref. 45 have been used and are given in the last column of the table. The results for the adjusted parameters are given in columns 2-4 of Table I.…”

Section: Dispersion Of the Refractive Indexmentioning

confidence: 99%

Refractive index of the alkali halides.mI. Constant joint density of states model

Johannsen

1997

Phys. Rev. B

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The electronic contribution to the imaginary part of the dielectric function of the alkali halides is assumed to be proportional to E Ϫ2 above the onset of optical absorption, which is equivalent to the assumption of a constant joint density of states ͑CJDOS͒ model. In this approach the electronic contribution to the refractive index can be described by two parameters, the long-wavelength limit of the refractive index n ϱ and the frequency of the onset of optical absorption E x0 . Various fits of the corresponding model function to experimental dispersion data show that E x0 is closely related to the frequency of the lowest exciton. Exciton absorption and interband transitions from the p valence bands to s and d conduction bands make the main contributions to the imaginary part of the dielectric function. The relative shifts of the s and d bands with respect to the p bands with density have different signs, and make different contributions to the photoelastic behavior. The CJDOS model is extended to account for the different behavior of s and d bands, and it is shown that the available literature data for the density dependence of the refractive index can be related to the energies of the s and d bands, derived from optical spectra and band-structure calculations. Shock data for LiF and NaCl are discussed, as well as low-pressure results for KCl, KBr, and KI. Recent high-pressure results for CsI show a strong nonlinear density dependence of the refractive index, in contrast to the almost linear behavior of the lighter alkali halides. Within the CJDOS model, this nonlinear behavior can be related to the closure of the band gap in CsI. ͓S0163-1829͑97͒06011-6͔

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“…TO vibrations describe the relative movement of the anion sublattice against the cation sublattice independent of long-range electrostatic forces. The optical measurements by Lowndes and Rastogi [3] give the results TryTo = -0.94 x lo-'' Pa-' for NaCl and Tr yTo = -0.37 x lo-'' Pa-' for LiF which are about a factor of four smaller than the results from ionic conductivity. This demonstrates an enlarged anharmonicity of the ionic vibrations in the neighborhood of a vacancy.…”

Section: Discussionmentioning

confidence: 75%

Uniaxial Stress Dependence of the Ionic Conductivity of Some Alkali Halides

Barth

Mohler

1993

Physica Status Solidi (b)

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A sensitive method to measure ionic conductivity changes of uniaxially stressed crystals is described. The stress effect in the extrinsic regime of the conductivity of NaCl and LiF single crystals is used to determine the elastic dipole tensor ofa migrating cation vacancy. The elastic dipole tensor is transformed to the double force tensor which gives insight into the jump path the ion takes and into the elastic displacements in the immediate neighbourhood of the jumping ion.Es wird ein empfindliches Verfahren zur Messung von Anderungen der Ionenleitfahigkeit einachsig belasteter Kristalle beschrieben. Aus dem Druckeffekt in dem Gebiet der extrinsischen Leitfahigkeit von NaCl-und LiF-Einkristallen wird der elastische Dipoltensor einer diffundierenden Kationenleerstelle bestimmt. Der elastische Dipoltensor wird in den Kraftdipoltensor transformiert, der Einsicht in den Sprungweg des Ions und in die elastischen Verformungen in der unmittclbaren Nachbarschaft des springenden Ions gewahrt.

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Temperature and pressure dependence of the transverse-optic modes of ionic crystals and their associated anharmonic self-energies

Cited by 89 publications

References 37 publications

Speculations on the absorption and emission properties of the F-centre in alkali halides

Speculations on the absorption and emission properties of the F-centre in alkali halides

Refractive index of the alkali halides.mI. Constant joint density of states model

Uniaxial Stress Dependence of the Ionic Conductivity of Some Alkali Halides

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